Preparation of ketones

ABSTRACT

A METHOD FOR PRODUCING KETONES BY CONTACTING AN N-PARAFFIN HAVING FROM 3 TO 25 CARBONS ATOMS WITH A NITRATING AGENT SELECTED FROM THE GROUP CONSISTING OF N2O3 AND A P2O5-NHO2-H2O COMBINATION IN THE PRESENCE OF AN OXYGEN CONTAINING GAS AT TEMPERATURE BETWEEN-52 AND 50*C. THE PRESENCE OF OXYGEN FUNCTIONS AS A NITRATION DIRECTOR FAVORING THE PRODUCTION OF KETONES.

United States Patent 01 hce Patented Dec. 28, 1971 3,631,110 PREPARATION OF KETONES Richard D. Smetana, Beacon, N.Y., assignor to Texaco Inc., New York, N.Y. No Drawing. Filed Oct. 29, 1968, Ser. No. 771,599 Int. (ll. C07c 45/02 U.S. Cl. 260-597 R 5 Claims ABSTRACT OF THE DISCLOSURE A method for producing ketones by contacting an n-parafiin having from 3 to 25 carbon atoms with a nitrating agent selected from the group consisting of N and a P O HNO -H O combination in the presence of an oxygen containing gas at temperatures between 50 and 50 C. The presence of oxygen functions as a nitration director favoring the production of ketones.

This invention relates to the production of ketones and more particularly to the production of ketones having from 3 to 25 carbon atoms by the nitration of normal paraf'finic hydrocarbons at low temperatures.

Heretofore, the nitration of paraffins employing such nitrating agents, as white fuming nitric acid, or nitrogen pentoxide has yielded primarily mixtures of alkyl nitrates and nitroparaffins depending upon the temperature and solvent employed. In general, yields of alkyl nitrates were as high as 83 percent while yields of nitroparafiins were of the order of 40 percent or more.

It has now been found and this constitutes my invention, a method whereby ketones can be produced in relatively high yields such that the nitration of paraffinic hydrocarbons under the conditions more fully described below undergo increased selectivity to ketone products while concomitantly diminishing the selectivity to nitroparafiins and alkyl nitrates.

It is therefore an object of this invention to provide a process for converting normal paraffins to ketones.

Another object of this invention is to provide a process for converting C to C normal parafiins to ketones in high yields.

Other objects and advantages will become apparent from a reading of the following detailed description and examples.

Broadly, this invention contemplates a method for preparing ketones which comprises contacting an n-paraffin having from 3 to 25 carbon atoms with dinitrogen pentoxide prepared either outside or in reaction situs via the dehydration of HNO by P 0 or the low hydrates thereof in the presence of an oxygen-containing gas at a temperature between 50 and 50 C. It has been discovered that the presence of oxygen in said method selectively directs the reaction to the production of ketones at the expense of nitroalkanes and alkylnitrates.

The n-paraffins contemplated for conversion to ketones under the nitration conditions recited herein are straight chain aliphatic hydrocarbons having from 3 to 25 carbon atoms. Such hydrocarbons include propane, butane, pentane, decane. dodecane, tetradecane, pentadecane, octadecane, eicosane, docosane, pentacosane and mixtures thereof. Typical paraflin hydrocarbon mixtures applicable to this invention include hydrocarbons containing from to 13 carbon atoms which may be obtained for example by absorption in molecular sieves or such other processes as urea or solvent dewaxing which are capable of recovering n-paraffin from mixtures of isoparaffins, naphthenes, aromatics or other normal paraffins.

The nitration of the paraffinic hydrocarbons contemplated herein to ketones under the conditions set forth is conducted in a liquid phase. In practice, the n-parafiin may itself constitute the reaction medium or solvents such as trifluoroacetic acid, nitromethane, acetonitrile, carbon tetrachloride, acetic anhydride, or 1,1,2-trichloro-1,2,2-trifluoroethane and may be employed. Solvents are preferably employed and function to increase the rate of ketone production. In general, applicable solvents include those materials which are stable under the instant reaction conditions and particularly those solvents which exhibit some tendency towards dissolution of both the hydrocarbon and the contemplated nitrating agent. In addition, highly preferred solvents as nitromethane, acetonitrile and carbon tetrachloride substantially enhance the rate of conversion in that reaction times are shortened by factors of 4.7, 3.9 and 3.4 respectively. In another instance, another highly preferred solvent, trifluoroacetic acid, affects selectivity in that nitroalkane formation is suppressed. Advantageously, I employ from 1 to 10 moles of solvent per mole of paraffin.

The paraffin conversion reaction described above either in the presence or absence of added solvent is undertaken by the interaction of a 2-phase liquid system. To assist the interaction of the phases agitation is provided such that the paraffin phase and the nitrating agent phase are brought into intimate contact. When solvents of the described type are employed partial solubility of the paraffin and nitrating agent in the solvent is provided thereby promoting better contact between the reactants.

It has been found that the selectivity of the reaction between nitrating agent and the normal paraffin can be modified such that under low temperature reaction conditions conversion to ketones is favored while concomitantly reducing the yield of nitroalkanes and alkylnitrates. By employing oxygen or an oxygen-containing gas, such as air, the selectivity of the formation reaction is altered in favor of ketones at the expense of nitro and nitrate products.

The nitration reaction outlined above proceeds by contacting the n-paraffin in the presence of an oxygen containing gas with a nitrating agent selected from the group consisting of N 0 and a combination of said combination having a P O /HNO /H O mole ratio between about 1/1/0 and 1/5/3, preferably between l/2/0 and 1/1/2. Under advantageous conditions the mole ratio of HNO to parafiin reactant is between about 6:1 and 1:10, preferably between 2:1 and 1:5. The mole ratio of oxygen to parafiin is at least 1:1 and preferably between 10:1 and 100:1, any excess oxygen being recycled to the reaction where continuous and circuitous processing is contemplated. The reaction progresses at temperatures ranging from about --50 to 50 C., preferably 0 and 30 C. under pressures of from 1 to 100 atmospheres, preferably 1 to 5 atmospheres.

The nitrating P O HNO H O combination as defined represents a mixture of HNO and P 0 or HNO and the lower hydrates of P 0 such as metaphosphoric acid (P O /H O mole ratio=1:1) and polyphosphoric acid (P O /H O mole ratio:1:l.6). The P 0 and hydrates thereof, within the limits defined function to dehydrate the HNO to N 0 The most preferred species of the P O HNO -H O nitrating agent combination is anhy drous i.e. when the P O /H O ratio is 1/0. In connection with the above inasmuch as water associated with the nitric acid employed is included in the water content designation of the combination, the employment of nitric acid is preferred although more dilute (i.e., more aqueous) nitric acid, e.g., as low as about 70 Wt. percent may be utilized.

In practice the reaction proceeds by adding for example a nitric acid-phosphorous pentoxide mixture within the mole ratio stated above to form. in situ dinitrogen pentoxide followed by parafiin addition, solvent addition where desired and thereafter oxygen is admitted through the agitated mixture at the rates outlined above. Vigorous agitation is applied to insure intimate contact between the parafiin and nitric acid-phosphorus pentoxide phases. The order of reactant addition however is not to be construed as critical and the materials may be added singularly or simultaneously. The reaction yielding a mixture of ketones, nitrates and unconverted paraffin is effectively accomplished within, for example, 1 to 3 hours. When solvents of the type previously described are employed, the rate of conversion is increased such that the reaction time may be substantially reduced to, for example, fractions of an hour.

Under the preferred conditions, the reaction is conducted until no more than about 50 mole percent preferably not above 40 mole percent of the paratfin is converted into derivative products comprising predominantly ketones with lesser amounts of alkyl nitrates and nitroalkanes. Above 50 mole percent conversion, cleavage and production of carboxylic acids result thereby decreasing selectivity to the desired ketones.

The unconverted reactants and products are recovered by standard means such as removing the volatile reactants and by-products such as N HNO and oxygen by distillation leaving a two-layer residue. The upper layer of said residue comprises the organic nitration products and unreacted paraffin and the lower layer phosphoric acid by-product. The two layers may then be separated by gravity separation and, if desired, the alkyl nitrates can be partially converted to ketones under basic conditions leaving a high concentration of ketones in the presence of parafiin and alcohol. Recovery of the ketone may be effectuated by selective extraction and/or fractional distillation. In continuous operation, unreacted paraifin and by-products such as nitric acid and oxides of nitrogen along with any solvent and oxygen, may be recycled for reintroduction along with fresh reactants after dehydration and reoxidation of the nitrogen oxides.

Ketones produced according to the instant process include propanone, butanone, hexanones, decanones, dodecanones, tetradecanones, pentadecanones, octadecanones, eicosanones, docosanones and pentacosanones. When mixed paraffins are contemplated as starting materials, such as C to C paraffins, mixed C to C ketones are produced which if desired may be individually recovered by fractionation subsequent to the separation and recovery procedure described above.

Ketones produced according to this process may be employed as antifoaming agents, solvents and torque fluids.

The following examples are illustrative of the invention but the scope of the invention is not to be limited thereby.

EXAMPLE I To a 100 milliter, 3-neck fiask fitted with a condenser, thermometer and stirrer, there was charged the following: nitrating agent, dodecane and when employed, oxygen. The oxygen, when admitted. was bubbled through the stirred mixture at the rate of 600 ml./ min. 40 moles of oxygen per mole of dodecane) and a water bath was employed to insure constant temperature throughout the reaction time. At the completion of the reaction time, the mixtures aqueous layer was separated from the organic layer by pouring the reaction mixture over ice and thereafter washing the organic layer with water. The organic layer was dried over anhydrous magnesium sulfate. The organic residue was analyzed utilizing infrared spectrometry and gas chromatography.

The foregoing procedure was employed in three runs utilizing varying reactants, quantities and reaction conditions. The particular run data and results are reported below in Table I.

TABLE I Run A B C Reaetants:

38. 4 7. 7 7. 7 10. 2 20. 4 20. 4 0.9 1. 8 1. 8 P205, :2 2 16. 4 16. PQO5/HNO3/H2O, mole ratio 1/2. 8/1 1/2. 8/1 1/2. 8/1 Ozlhydrocarbon, mole ratio 40/1 llNOg/hydroearbon, mole ratio- 72/1 7.2/1 7. 2/1 Reaction conditions:

'lime, minutes 60 Temperature, 0.. 25 5 25 Product yield: Percent conversion 32. 5 3. 8 16. 6 Percentselectivity:

Nitrate 37 78 63 Nitroalkane. 4 22 37 Ketone 59 0 0 As can be seen from the above Table I, the effectiveness of oxygen enhanced the extent of conversion and directed the reaction toward the formation of ketones. In Run A, while only the amount of nitrating agent was employed there resulted a two fold increase in conversion. Further, in the presence of oxygen, Run A demonstrates that oxygen functions as a nitration director favoring the production of ketones at the expense of both nitroalkane and alkylnitrate.

I claim:

1. A method for preparing ketones which comprises contacting in the liquid phase an n-parafiin having from 3 to 25 carbon atoms in the presence of an oxygen containing gas with a nitrating agent selected from the group consisting of dinitrogen pentoxide and a P O -HNO -H O combination, said combination having a P O /HNO /H O mole ratio between about l/l/O and 1/5/3 at a temperature from about 50 to 50 C. under a pressure of from about 1 to 100 atmospheres utilizing a mole ratio of oxygen to said n-paraffin of at least 1:1 to 100:1 and a mole ratio of HNO to said paraffin of between about 6:1 and 1:10.

2. A method according to claim 1 wherein said temperature is between about 0 and 30 C., said nitrating agent in said P O HNO --H O combination of a mole ratio between about 1/2/0 and 1/1/2, said oxygen to said n-paraffin mole ratio is between 10:1 and 100:1 and said HNO to said n-paraffin mole ratio is between 2:1 and 1:5.

3. A method according to claim 1 wherein said oxygen containing gas is oxygen.

4. A method according to claim 1 wherein said n-paraffin is dodecane.

5. A method according to claim 1 wherein said contacting is conducted in the presence of from 1 to 10 moles of solvent per mole of n-paraffin, where said solvent is selected from the group consisting of nitromethane, ace tonitrile, carbon tetrachloride, and trifluoroacetic acid.

References Cited UNITED STATES PATENTS l0/l957 Cottle et al. 260-597 R 10/1957 McKinnis 260-597 R BERNARD HELFIN, Primary Examiner US. Cl. X.R. 260467, 644 

